Thermoplastically processible polyamides can be divided into semicrystalline and amorphour homo- and copolyamides.
The semicrystalline polyamides form an important group of commercial thermoplastics. Shaped articles produced from them are distinguished by high strength, rigidity, toughness, surface hardness, good abrasion behavior, and excellent resistance to chemicals and stress-crack resistance. However, the usefulness of these semicrystalline homo- and copolyamides, for example the high melting point polyamides PA 6 and Pa 6,6, is substantially reduced by their tendency to absorb water and the associated reduction of the glass transition temperature resulting in loss of rigidity and strength.
Rigid amorphous copolyamides are generally produced from aromatic dicarboxylic acids and diamines having crystallization-inhibiting structures, and can contain further comonomers such as amino acids, lactams, and salts of diamines and dicarboxylic acids. The properties of such copolyamides can be intentionally varied within wide limits by the choice of monomers used in each case.
As already mentioned, the glass transition temperature drops due to moisture absorption, which in turn causes a reduction of the upper use-temperature. The temperature of use of molded bodies is greatly reduced, leading to a considerable limitation in their utility.
Amorphous copolyamides are described, for example, in the following patents: GB 619,707, CH 449,257, U.S. Pat. No. 2,494,563, U.S. Pat. No. 3,842,045, U.S. Pat. No. 3,840,501, JP 72/11,502, U.S. Pat. No. 2,969,482, U.S. Pat. No. 3,597,400, DE 21 59 803, and CH 624,970.
It is also known to use polymeric--in particular dimerized--fatty acids for the production of polyamides and copolyamides. These materials are used, for example, in adhesive and lubricant polymer chemistry. The structure and properties of dimerized fatty acids are described in detail in, for example, the Henkel-Emery/Gouda (NL) brochure entitled "Empol Dimer and Polybasic Acids, Technical Bulletin 114". These dimerized fatty acids are obtained from monomeric unsaturated fatty acids usually containing 18 carbon atoms by a specific polymerization reaction. There are many products having different ratios of monofunctional, difunctional, trifunctional, and polyfunctional acids. Types having a high dimer content, for example 90%, in particular 97%, are preferred for the production of thermoplastic polyamides.
CA 8 61 620 describes polyamides derived from 1-amino-3-aminomethyl-3,5,5-trimethylcyclohexane; optionally further diamines and, in particular, at least 25 mol % of dimerized fatty acids, based on all acid components (sebacic acid being the preferred dicarboxylic acid) are included. However, these known copolyamides have low rigidity. The influence of aromatic dicarboxylic acids on the glass transition temperature Tg and rigidity, in particular in molar amounts of more than 25%, based on all acids, is not relevant in this CA-PS, because the copolyamides described are used for the preparation of flexible products such as binders, shoe adhesives, and films.
Thermoplastically processible plastic materials which have high rigidity and strength and which maintain these properties under the influence of moisture (high atmospheric humidity or contact with water) are required for many commercial applications. Preferably, the moisture absorption should be low enough so that the glass transition temperature is affected as little as possible.